Water proofing membrane, and a method for making a water proofing membrane

ABSTRACT

The invention relates to a waterproofing membrane ( 1 ) comprising a structure incorporating a fiber layer ( 10 ) and carrying a bituminous mass ( 15 ) on one side, the other side carrying a layer ( 20 ) of a first substance comprising between 10% and 40% by dry weight of an acrylic polymer mixed with between 4% and 40%, preferably between 20% and 40%, by dry weight of titanium dioxide and at least 1% by dry weight of a transparent or translucent hydrophobic material, said layer ( 20 ) defining a surface (S) of said membrane ( 1 ).

FIELD OF THE INVENTION

The present invention relates to a water proofing membrane, such as for application on a building roof, comprising a structure incorporating a fibre layer, such as a glass fiber web, carrying a bituminous mass on one side and where the other side of the fiber layer has a substance comprising titanium dioxide and an acrylic polymer.

BACKGROUND OF THE INVENTION

Such a waterproofing membrane is known from WO 2004/070107. For manufacturing the known membrane, the bituminous mass is applied to the one side of the structure where on the other side a cover layer formed by a substance comprising particulate titanium oxide and an acrylic polymer has been applied. The substance is applied as a coating to the fiber layer before the bituminous mass is applied. The acrylic polymer reduces exudation, as discussed also in EP 876 532 and EP 1 252 386, which would otherwise give rise to brown stains forming on the upper side of the membrane. The acrylic polymer also forms to some extend a barrier against ultraviolet rays so that the latter cannot easily reach the bituminous mass. Therefore the bituminous mass keeps its waterproofing and protective properties for a longer time and exudation is reduced in that substantially less oil of the bituminous mass will migrate through the membrane to the upper side when in use. In such a manner, less pollution is provoked as the oil will remain in the bituminous mass and not mix with rain water.

As standards have changed it is sometimes preferred that water proofing membranes, when applied to a roof, have reflective properties in order to reflect incident sunlight and cause in such a manner less heat to be absorbed by the bituminous mass and the building structure covered by the waterproofing membrane. Hence, WO 2004/070107 proposes that the aforementioned acrylic polymer should comprise titanium dioxide, which is an appropriate reflective material, to be integrated in the acrylic polymer matrix which is applied to the surface of the fiber layer and which penetrates partially therein before the bituminous mass is applied. The presence of titanium dioxide in the substance brings about a white surface of the membrane thus leading to lower temperatures reached by the bituminous mass when exposed to sunlight. This enables in its turn use of the bituminous mass with a further reduced risk of oil migration, or exudation, and the titanium dioxide and the UV resistant acrylic polymer are anchored in the structure and cannot be easily removed for example by the rain. The coating of the aqueous mixture of the acrylic polymer and the titanium dioxide is applicable by impregnation or induction to the structure, thus causing a structural bound between the layer and the structure.

OBJECT OF THE INVENTION

For cost and environment reasons it is desirable to reduce as much as possible the use of the acrylic polymer. Laboratory testing may be performed whereby the membrane is subjected to various degrees of solar exposure, and the amount of acrylic polymer is selected such that exudation will likely not occur. However, in practical use of the membrane local brown stains may sometimes nevertheless appear on the visible surface, due to oils locally migrating from the opposite side of the membrane.

The present inventors have found that this exudation problem arises through a strong local or spot-wise heat absorption, and have identified the cause to be dark spots of dirt that appear on the upper side of the membrane after some time of use due to its exposure to the environment. In fact, over the time dirt in the form of particles settling on the entire surface of the membrane will lead to a darkening of the membrane, reducing the reflective effect of the titanium dioxide. Such a darkening, whether it is spot-wise or a uniform darkening across the entire surface, leads to an increased heat absorption and, hence, to the risk of a consequential oil migration leading to brown spots that in in themselves will make the problem of heat absorption worse over time.

Hence, an object of the invention is to seek to eliminate or reduce the tendency of oil migration while allowing for a possible reduction in the thickness of the layer of acrylic polymer/titanium dioxide.

SUMMARY OF THE INVENTION

The inventors have found that by adding water-repellent properties to the membrane, dirt which may otherwise give rise to the aforementioned stains, is more easily washed away from the membrane surface, thus reducing the tendency of the formation of local brown spots due to migrating oils that darken the white surface of the membrane. Hence, with the invention local exudation is less likely to occur.

More specifically, according to the invention on the side opposite the bituminous mass there is carried a layer of a first substance comprising between 10% and 40% by dry weight of acrylic polymer mixed with between 4% and 40%, preferably between 20% and 40%, by dry weight of titanium dioxide and at least 1% by dry weight of a transparent or translucent hydrophobic material, said layer defining a surface of the membrane. The layer of the first substance may have been applied as a uniform layer, and preferably has a thickness of 100 μm-200 μm.

The invention also relates to a method of making a water proofing membrane including the aforementioned layer of a first substance, including the steps of i) preparing the first substance by mixing an acrylic polymer with titanium dioxide and with the hydrophobic material under agitation, preferably by separately adding these ingredients to a mixer, such that the acrylic polymer and the hydrophobic material forms a matrix for the titanium dioxide, and ii) applying a layer of said first substance onto a first side of a fiber layer, and iii) applying a bituminous substance onto a second side of said fiber layer.

Preferably, the hydrophobic material is selected such that a drop of liquid water in contact with the upper surface of the membrane has a contact angle θ_(c) greater than 90°, as measured according to contact angle meter (optical tensiometer), preferably greater than 95°.The contact angle quantifies the wettability of the solid surface by a liquid: if the contact angle is large, the drop of liquid will bead up. Highly hydrophobic surfaces resulting from the use of low surface energy materials may have water contact angles as high as ˜120°. By way of example, the hydrophobic material may chosen from the group consisting of carnauba, polyethylene, paraffin wax emulsions, polysiloxanes emulsions and fluorosurfactants. Silicone may also be envisaged. An anionic paraffin/polyethylene wax emulsion has shown very good properties.

Preferably, the first substance comprises between 1% and 5% by dry weight of the hydrophobic material.

The first substance may comprise between 1% and 5% by dry weight of a polyurethane polymer, in order to decrease water absorption and increase outdoor durability further.

According to one embodiment of the waterproofing membrane according to the invention, the first substance may comprise between 30% and 50%, preferably approximately 40%, by dry weight, of mineral filler being a mixture of talc, calcium carbonate and aluminium hydroxide.

Calcium carbonate is a suitable filler which does not adversely affect the reflective properties of titanium dioxide.

A first substance having the particular compositions defined in the dependent claims have been found to provide even further beneficial properties in terms of durability and resistance to exudation.

The bituminous mass may include an Atactic Polypropylene (APP), an Atactic Poly Alpha Olefin (APAO) or a Thermoplastic Polyolefin (TPO). The bituminous mass may comprise SBS.

The fibre layer, such as for example a glass fibre, could by way of example be a non-woven as well as a woven structure. The structure could also be a composite structure formed by glass fibres and a glass grid, a polyester grid or non-woven polyester. A removable foil may be applied on the bituminous mass, to allow for the membrane to be rolled-up for storage.

For manufacturing reasons it may be such that, compared to the aforementioned bituminous mass that defines the opposite surface of the membrane, a bituminous material with a different composition, such as to make it more fluid, is used to impregnate the fibre layer as such, although often only the one and same bituminous mass will also impregnate the fibre layer.

The acrylic polymer composition referred to may be of one brand; alternatively the acrylic polymer may be prepared by mixing acrylic polymer products supplied by different manufacturers.

BRIEF DESCRIPTION OF THE FIGURES

The water-proofing membrane according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

Fig. a is a schematic cross-sectional view of a first embodiment of the membrane of the invention,

Fig. b is a schematic cross-sectional view of another membrane that does not fall within the appended claims,

Fig. c is a schematic cross-sectional view illustrating a welded overlap between two membranes as shown in fig. b, and

Fig. d illustrates the conventional definition of certain parameters used in the present text.

DETAILED DESCRIPTION OF AN EMBODIMENT

Fig. a shows a waterproofing membrane 1 comprising a structure incorporating a fibre layer 10 and carrying a bituminous mass 15 on the side to be arranged in contact with a building structure, the other side carrying a layer 20 of a substance comprising acrylic polymer mixed with titanium dioxide and a transparent or translucent hydrophobic material, the layer 20 defining the surface S of the membrane 1 that is exposed to the weather. The transparent or translucent nature of the hydrophobic material allows for the titanium dioxide pigment to be distinguishable such that the membrane appears white, the titanium dioxide giving light and heat reflective properties to the membrane. A suitable method of making the substance, also referred to in the appended claim 1 as the “first substance”, includes the steps of adding the acrylic polymer, the titanium dioxide and the hydrophobic material separately to a mixer under continued agitation.

An example of a method for applying a bituminous mass to the other side of the fiber layer 10 is given in WO 2004/070107.

The following table gives an example of the composition of a first substance according to the present invention applied as the layer 20 of fig. a, where:

Ecodis P90 (Polyacrylate ammonium salt) is a dispersing agent,

Byk024 is a mixture of foam destroying polysiloxanes and hydrophobic solids in polyglycol and acts as an anti-foaming agent,

Luzenac 00C (talc) acts as a filler,

Durcal 1 and Durcal 10 (Calcium carbonate) is a filler to increase hardness of coating,

Martinal On-310 (Aluminium hydroxide) is a fire retardant,

Tronox 2160 (Titanium dioxide) is a white pigment,

Acronal 290D and Joncryl U6336 (an aqueous dispersion of a polymer based on acrylic ester, styrene, and a free aliphatic polyurethane acrylic hybrid, respectively) are binders for outdoor durability and water adsorption,

Texanol (Ester Alcohol (2,2,4-Trimethyl-1,3-pentanediol Monoisobutyrate)) is a coalescent agent,

Fongal PZT (Terbutryn (13.4%)+ZnPT (13.4%)) is a biocide,

Nuosept BMC-422 (a synergistic blend of BIT, MIT and very low levels of CIT) may act as a preservative,

MichemEmulsion 36840E (anionic paraffin/polyethylene wax emulsion) is a surfactant agent, and

Rheotech 3800 (anionic paraffin/polyethylene wax emulsion) is a thickener.

The contact angle, discussed also below, when using the above composition was determined in a laboratory using the contact angle meter to be θ_(c)=93° for the membrane surface S; a similar test without the hydrophobic material (MichemEmulsion 36840E) showed a value of θ_(c)=81°.

Addition of the ingredients took place according to the indicated sequence, concluding with addition of the hydrophobic material and then performing an adjustment of the pH-value if required, with the duration of the individual mixing steps being as indicated in the table.

FORMULATION Mixing process Dry weight (%) 1. Additives Ecodis P90 5-10′ 0.35 Water (disperser) 0.00 Byk024 1.35 2. Fillers and pigments Luzenac 00C 35-45′ 8.81 Durcal 1 à 2500 tr/min 1.76 Durcal 10 (glass beads) 7.05 Martinal On-310 25.35 Tronox 2160 28.14 3. Binder Acronal 290D 5-10′ 20.30 Joncryl U6336 3.85 4. Rest of the additives Texanol 5-10′ 1.49 Fongal PZT 0.55 Nuosept BMC-422 0.01 MichemEmulsion 36840E 1.00 5. Adjustment (Visco, pH, dry content) Water ES = 75 ± 1% Ammonia pH = 8-9 Rheotech 3800 FILTRATION Visco = 25000- 3000 cps

Fig. b shows a water proofing membrane that does not fall within the appended claims and which comprises a structure incorporating a fibre layer 10 and carrying a bituminous mass 15 on one side, the other side carrying a first layer 25 of a second substance different from the substance referred to above with reference to fig. a and comprising an acrylic polymer mixed with titanium dioxide, such as in the proportions disclosed in WO2004/070107 (including table 1 and claims 1 and 2 therein), and a second layer 28 of a transparent or translucent hydrophobic material on the second substance, the hydrophobic material, which may have been chosen from the group consisting of carnauba, polyethylene, paraffin wax emulsions, polysiloxanes emulsions and fluorosurfactants, having been applied as a uniform layer and defining the upper surface S of the membrane 1 that is exposed to the weather.

Fig. c illustrates a welded overlap between two membranes as shown in fig. b.

Referring now to fig. d and denoting the solid/vapor interfacial energy as γ_(SG), the solid/liquid interfacial energy as γ_(SL) and the liquid/vapor interfacial energy (i.e. the surface tension) as γ, Young's equation requires the following to be satisfied in equilibrium:

0=γ_(SG)−γ_(SL)−γ cos θ_(C)

where θ_(c) is the contact angle.

The contact angle is the angle, conventionally measured through the liquid, at which a liquid interface meets a solid surface. It quantifies the wettability of the solid surface by a liquid: if the contact angle is small, a drop of the liquid will spread on the solid; if the contact angle is large, the drop of liquid will bead up. If the molecules of a liquid are strongly attracted to the molecules of a solid then a drop of the liquid will completely spread out on the solid surface, corresponding to a contact angle of 0°. Weaker attractions between liquid and solid molecules will result in higher contact angles. Generally, if the water contact angle is larger than 90°, the solid surface is considered hydrophobic.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Also, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous. 

1. A waterproofing membrane comprising a structure incorporating a fiber layer and carrying a bituminous mass on one side, the other side carrying a layer of a first substance comprising between 10% and 40% by dry weight of an acrylic polymer, mixed with between 4% and 40% by dry weight of titanium dioxide and at least 1% by dry weight of a transparent or translucent hydrophobic material, said layer defining a surface of said membrane.
 2. The waterproofing membrane of claim 1, wherein said layer of said first substance comprises between 30 g/m² and 120 g/m² of said acrylic polymer, between 12 g/m² and 120 g/m² of said titanium dioxide and at least 3 g/m² of said hydrophobic material.
 3. The waterproofing membrane of claim 1, wherein said hydrophobic material is selected such that a drop of liquid water in contact with said surface of the membrane has a contact angle θ_(c), measured in accordance with contact angle meter (name of test) greater than 90°, such as in the order of 93°-100°.
 4. The waterproofing membrane according to claim 1, wherein said first substance comprises between 1% and 5% by dry weight of a polyurethane polymer.
 5. The waterproofing membrane according to claim 4, wherein said layer of said first substance comprises between 3 g/m² and 15 g/m² of said polyurethane polymer.
 6. The water-proofing substance according to claim 1, wherein said hydrophobic material is chosen from the group consisting of carnauba, polyethylene, paraffin wax emulsions, polysiloxanes emulsions and fluorosurfactants.
 7. The water proofing-membrane according to claim 1, wherein said first substance comprises between 10% and 25% by dry weight of said acrylic polymer mixed with between 20% and 30% by dry weight of titanium dioxide.
 8. The water proofing-membrane according to claim 7, wherein said layer of said first substance comprises between 30 g/m² and 75 g/m² of said acrylic polymer and between 60 g/m² and 90 g/m² of said titanium dioxide.
 9. The waterproofing membrane according to claim 1, wherein said first substance comprises between 18% and 23% by dry weight of said acrylic polymer and between 25% and 30% by dry weight of said titanium dioxide.
 10. The water proofing-membrane according to claim 9, wherein said layer of said first substance comprises between 50g/m² and 70 g/m² of said acrylic polymer and between 75 g/m² and 90 g/m² of said titanium dioxide.
 11. The waterproofing membrane according to claim 1, wherein said first substance comprises between 1% and 5% by dry weight of said hydrophobic material.
 12. The water proofing-membrane according to claim 11, wherein said layer of said first substance comprises between 3 g/m² and 15 g/m² of said hydrophobic material.
 13. The waterproofing membrane according to claim 1, wherein said first substance further comprises between 30% and 50% by dry weight of mineral filler being a mixture of talc, calcium carbonate and aluminium hydroxide.
 14. The water proofing-membrane according to claim 13, wherein said layer of said first substance comprises between 90 g/m² and 150 g/m² of said mineral filler.
 15. The waterproofing membrane according to claim 1, wherein said bituminous mass comprises an atactic polypropylene, an atactic poly alpha olefin or a thermoplastic polyolefin.
 16. The waterproofing membrane according to claim 1, wherein said bituminous mass comprises styrene butadiene styrene.
 17. The waterproofing membrane of claim 16, wherein said styrene butadiene styrene comprises at least approximately 8% of a thermoplastic elastomer.
 18. The waterproofing membrane according to claim 1, including a plastic foil or other protective layer on said bituminous mass.
 19. A method of making a water proofing membrane with a layer of a first substance according to claim 1, including the steps of i) preparing said first substance by mixing said acrylic polymer as a suspension, dispersion or solution with said titanium dioxide and with said hydrophobic material in liquid form, such that said acrylic polymer and said hydrophobic material form a matrix for said titanium dioxide, ii) applying said first substance as a layer onto a first side of said fiber layer, and iii) applying said bituminous substance onto a second side of said fiber layer.
 20. The method of claim 19, wherein said acrylic polymer, said titanium dioxide and said hydrophobic material are added separately to a mixer under agitation, preferably adding the hydrophobic material lastly. 